Does this study really mean that "diet soda may not be the optimal substitute for sugar-sweetened beverages for protection against vascular outcomes," as the lead author is quoted as saying?

As Rosie Mestel puts it:

It's worth noting, as some scientists did, that this is a link, not proof of cause and effect. After all, there are many things that people who slurp diet sodas every day are apt to do—like eat a lousy diet—and not all of these can be adjusted for, no matter how hard researchers try. Maybe those other factors are responsible for the stroke and heart attack risk, not the diet drinks. (Those who drink daily soda of any stripe, diet or otherwise, are probably not the most healthful among us.)

Leaving questions about the accuracy of dietary information obtained by questionnaire, the study raises more important questions:

1. Could this finding simply be a statistical result of a "fishing expedition?" The food frequency questionnaire undoubtedly asked hundreds of questions about diet and other matters. Just by chance, some of them are going to give results that look meaningful. The increase in stroke risk seems astonishingly high and that also suggests a need for skepticism.

2. What is the mechanism by which diet sodas lead to stroke or heart disease? I can't think of any particular reason why they would unless they are a marker for some known risk factor for those conditions.

Please understand that I am no fan of diet sodas. I don't like the metallic taste of artificial sweeteners and they are excluded by my "don't eat" rule: never eat anything artificial.

But before I believe that this study means that artificial sweeteners cause cardiovascular problems, I want to see a study designed to test this particular hypothesis and a plausible biological reason for how diet sodas might cause such problems.